The long term objective of this proposal is to investigate the medicinal chemistry of alkyl-substituted gamma-butyrolactones (GBLs) and related compounds. These compounds have been shown to bind to the picrotoxin binding site of the gamma-aminobutyric acid (GABA) receptor/chloride ionophore complex where they function as either picrotoxin agonists, antagonists, or inverse agonists. They are useful experimental agents for investigations the role of GABAergic neurotransmission in nervous system function. Those compounds which act as picrotoxin antagonists and inverse agonists have potential as new therapeutic agents for the treatment of seizure disorders. Our specific aims are: 1) To characterize structure/activity relationships of additional alkyl- substituted GBLs and GBL analogs. We wish to determine further which structural characteristics of these molecules are responsible for their convulsant and anticonvulsant activity; their potency; their specific biochemical and cellular actions; and their sites of action in brain. We will synthesize several series of new compounds and have them evaluated in a variety of in vivo and in vitro assays. A steric analysis utilizing computer graphics will be made to correlate the structure of the molecules with their neuropharmacological activities. 2) To measure tissue concentrations of GBLs and GBL analogs. This will be accomplished by gas chromatographic analysis of tissue extracts. 3) To develop a method for detecting and quantitating low affinity binding sites for GBLs and GBL analogs in brain. The neuropharmacological activities of GBLs are characterized by low affinity interactions (10-3M to 10-4M) at the picrotoxin binding site, and possibly other sites in brain. Traditional radioligand binding methods are not suitable for studying such low affinity interactions. We will use 19F NMR to study the low affinity binding of GBLs in brain. Thus, we will synthesize fluorinated GBLs and GBL analogs and carry out 19F NMR studies with them in brain and other in vitro preparations so that the importance of these low affinity binding sites can be evaluated.